Gary - Here are some screen savers for Windows (not necessarily made for Windows 7, but they work fine under Win 7).

Really Slick Screensavers - These are free, and there are no added programs installed (none that I recall, anyway).

Seraline - These cost money, but they are pretty darn cool, IMO. The ones that use color cycling (Adrift, Seractal, and Seraline) don't seem to get along great with Win 7's Aero interface, but they work fine if you leave color cycling off. No extra stuff installed, either.